Conventionally, heat exchangers for use in air conditioning machines, air conditioners for automobiles, and the like are often formed from aluminum-containing metal materials from the perspective of advantages such as workability and thermal conductivity, and in order to increase the heat exchange efficiencies, the intervals between the aluminum-containing metal materials (generally referred to as fins) at blast sites are designed to be highly narrow. In the heat exchangers, dew condensation is caused through condensation of water in the atmosphere on the fins when the air conditioners are operated (cooled), and as the hydrophobicity of the fin surfaces are higher, the dew condensation water becomes bulky water droplets, thereby making clogging more likely to be caused between the fins. The generation of clogging increases the ventilation resistance and decreases the heat exchange efficiency, thereby failing to achieve the original performance of the heat exchanger. In addition, the clogging may also increase noises in blast. In order to solve these problems, methods of providing hydrophilicity to the surfaces of aluminum-containing metal materials and heat exchanger members have been proposed, and implemented (Patent Literature 1, Patent Literature 2, Patent Literature 3).
As the methods of providing hydrophilicity, hydrophilization treatment agents containing inorganic substances as their main constituents (hereinafter, referred to as inorganic hydrophilization treatment agents) (see Patent Literature 1, Patent Literature 2, and Patent Literature 3), hydrophilization treatment agents containing, as their main constituents, resins or organic substances such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylic acid (hereinafter, referred to as organic hydrophilization treatment agents), and the like have been proposed and implemented (see Patent Literature 4, Patent Literature 5, Patent Literature 6, Patent Literature 7, and Patent Literature 8).
In this regard, aluminum-containing metal materials and heat exchangers provided with hydrophilicity through the use of the inorganic hydrophilization treatment agents can sustain high hydrophilicity for a long period of time with excellent durability, but at the same time, have problems with odor properties, such as generation of film odors unique to the inorganic substances (dusty odors, hereinafter referred to as dust odors). On the other hand, when the organic hydrophilization treatment agents are used, the problems with dust odors are reduced, but at the same time, organic substances as hydrophilic constituents are likely to flow off, and it is thus difficult to sustain hydrophilicity over long period of time, thereby resulting in problems with durability. In order to remedy these problems, hydrophilization treatment agents have been proposed which have silica particles as inorganic substances dispersed in polyvinyl alcohol, thereby remedying dust odors unique to silica (see Patent Literature 9 and Patent Literature 10). However, films from the hydrophilization treatment agents with the silica particles simply dispersed in polyvinyl alcohol have the problem of generating dust odors as a result of exposing the silica particles due to the polyvinyl alcohol flowing off through long-term use.